Cell Plasma Membrane Structure and Function Adapted from site found on Internet

1. HOMEOSTASIS and the
PLASMA MEMBRANE
Mrs. Neistadt
BIOLOGY
Adapted from Mr. Young- Thanks
Mr. Young!!

2. Question:
What happens to the helium in a
balloon after a few days? Why?

3. Objectives
Explain the function of the plasma
membrane.
Relate the function of the plasma
membrane to the fluid mosaic model.
Create a model of the plasma
membrane

4. Homeostasis Key – BALANCE!
*Homeostasis
 *Theequilibrium of an organism’s internal
environment that maintains conditions
suitable for life.
 Example: Human sweating
• Helps body maintain its proper temperature.
Organisms must be able to adjust to
changes in their external environment.

5. Cells and Homeostasis
How do cells maintain a balance?
 *Cells control what materials enter and
leave the cell through the plasma
membrane.
PLASMA MEMBRANE

6. Plasma Membrane – Properties
 *The plasma membrane is selectively
permeable (semipermeable).
 *Allows some materials to pass.
Water, oxygen, carbon dioxide
 *Prevents others from passing.
Proteins, carbohydrates
• Different cells may be permeable to different chemicals
or substances.

7. Plasma Membrane – Structure
1. BILAYER (2 layers)
2. Each layer made of lipid
molecules
3. Protein molecules
embedded in bilayer

8. Phospholipid Bilayer
POLAR
blePhosphate
HEAD
olu Group
 Lipids e r-S
Wat
 Organic compounds Glycerol
Backbone
 Fats + Oils
 Non-polar
 Insoluble in water
(Not attracted to water) FATTY
ble
ACIDS
olu
Ins
 Phosphate Head
ater -
 Polar W
 Water-soluble
(Attracted to water)

9. QUESTION:
Most cells have a watery internal and
external environment. Given this
information, how might you expect the
phospholipids to be arranged?
OUTSIDE OUTSIDE
OR
INSIDE INSIDE

10. Do you “love” or “fear” water?
Hydrophilic heads
Water Loving
Hydrophobic tails
Water
Fearing

11. *Phospholipid Bilayer

12. *Fluid Mosaic Model *Phospholipid molecules may
move sideways through their layer.
 “FLUID”

13. Proteins
*Most of the functions of the plasma
membrane are carried out by proteins.
 Functions:
• Determine which particles can pass through
membrane
• Serve as enzymes (accelerate chemical reactions)
• Act as markers
– Help fight disease

14. Plasma membranes are like…
Can you think of any examples that are
similar to a plasma membrane?
 Example: Balloon lets out helium
 Example: Doorman to a building lets
everyone out but only tenants in

15. What would happen…
What would happen if the cell let
everything in?
What would happen if the cell let
everything out?
A balanced cell is a happy cell!!

16. Your turn…
Draw a picture of a plasma membrane
Show the bi-layer and label the parts.
Refer to pgs 188 and 190 in your text
Write a short summary of how the
plasma membrane works (same paper)
Use your new vocabulary words in your
summary

17. Create a model of a plasma membrane:
White marshmallows are the polar
heads
Colored marshmallows are the proteins
and cholesterol
Toothpicks are the non-polar tails.
Label the parts of the membrane
Be creative…and have fun!

18. Plasma Membrane – Functions
 NOT just a barrier surrounding the
cell.
1. Selectivity
2. Molecular recognition
3. Export of wastes and cell products
4. Import of nutrients
5. Ability to change in response to
environment